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Abstract:

An object of the present invention is to provide a turbine protection
device which can interrupt backflow from a deaerator to a turbine
completely even if a check valve provided between the deaerator and the
turbine can not interrupt the steam flow between the deaerator and the
turbine completely. In order to achieve the above object, a control unit
sends commands to a shutdown valve device so as to close the shutdown
valve device when a differential pressure resulted from subtracting a
pressure of a extraction steam from a pressure within the deaerator
becomes greater than or equal to a first predetermined value. As a
result, the backflow from the deaerator to the turbine is interrupted by
a stop valve of the shutdown valve device.

Claims:

1. A turbine protection device provided in a steam turbine system, the
steam turbine system comprising:a turbine driven by steam generated in a
boiler;a condenser to condense the steam exhausted from the turbine into
a condensate;a deaerator to store the condensate which is preheated by
being heated and deaerated;an inlet pipe to take the extraction steam for
heating and deaerating into the deaerator; anda check valve provided in
the inlet pipe, comprising:pressure gauge to measure pressure of the
extraction steam and pressure within the deaerator;a shutdown valve
device provided in the inlet pipe; andcontrol unit to control the
shutdown valve device using commands based on the pressure of the
extraction steam and the pressure within the deaerator,wherein the
shutdown valve device is opened and closed by the commands from the
control unit, and when the shutdown valve device is closed, the shutdown
valve device interrupts the steam flow from the deaerator to the turbine.

2. The turbine protection device according to claim 1, wherein the control
unitsends commands to the shutdown valve device so as to close the
shutdown valve device when a differential pressure resulted from
subtracting the pressure of the extraction steam from the pressure within
the deaerator becomes greater than or equal to a first predetermined
value which is set in advance, andsends commands to the shutdown valve
device so as to open the shutdown valve device when the differential
pressure becomes greater than or equal to a second predetermined value
which is set in advance.

3. The turbine protection device according to claim 1, wherein the control
unitsends commands to the shutdown valve device so as to close the
shutdown valve device when a first predetermined time has elapsed on
condition that a differential pressure resulted from subtracting the
pressure of the extraction steam from the pressure within the deaerator
is greater than or equal to a first predetermined value which is set in
advance after the differential pressure becomes greater than or equal to
the first predetermined value, andsends commands to the shutdown valve
device so as to open the shutdown valve device when a second
predetermined time has elapsed on condition that the differential
pressure is less than or equal to a second predetermined value which is
set in advance after the differential pressure becomes less than or equal
to the second predetermined value.

4. A method for controlling a steam turbine system, the steam turbine
system comprising:a turbine driven by steam generated in a boiler;a
condenser to condense the steam exhausted from the turbine into a
condensate;a deaerator to store the condensate which is prepared by being
heated and deaerated;an inlet pipe to take the extraction steam for
heating and deaerating into the deaerator; anda check valve provided in
the inlet pipe, comprising the steps of:measuring a pressure of the
extraction steam and a pressure within the deaerator;opening and closing
a shutdown valve device provided in the inlet pipe based on a
differential pressure between a pressure of the extraction steam and a
pressure within the deaerator; andinterrupting the steam flow from the
deaerator to the turbine by closing the shutdown valve device.

5. The method according to claim 4, wherein further comprising the steps
of:sending commands to the shutdown valve device so as to close the
shutdown valve device when a differential pressure resulted from
subtracting the pressure of the extraction steam from the pressure within
the deaerator becomes greater than or equal to a first predetermined
value which is set in advance, andsending commands to the shutdown valve
device so as to open the shutdown valve device when the differential
pressure becomes greater than or equal to a second predetermined value
which is set in advance.

6. The method according to claim 4, wherein further comprising the steps
of:sending commands to the shutdown valve device so as to close the
shutdown valve device when a first predetermined time has elapsed on
condition that a differential pressure resulted from subtracting the
pressure of the extraction steam from the pressure within the deaerator
is greater than or equal to a first predetermined value which is set in
advance after the differential pressure becomes equal to or greater than
or equal to the first predetermined value, andsending commands to the
shutdown valve device so as to open the shutdown valve device when a
second predetermined time has elapsed on condition that the differential
pressure is less than or equal to a second predetermined value which is
set in advance after the differential pressure becomes less than or equal
to the second predetermined value.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]The present application claims benefit of the filing date of
Japanese Patent Application No. 2009-189423 filed on Aug. 18, 2009 which
is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to a turbine protection device to
protect a turbine of a steam turbine system.

[0004]2. Description of Related Art

[0005]For example, a steam turbine system of an electric-power generating
steam turbine plant is provided with a deaerator to store a condensate
which is preheated by heating condensate exhausted from a condenser using
a extraction steam from a turbine so as to deaerate gases such as oxygen,
etc.

[0006]Also, during normal operation of the steam turbine system, a
pressure within the deaerator (a deaerator pressure) is decreased from a
pressure of the extraction steam (an extraction pressure) due to a
pressure loss of a path through which the extraction steam passes from
the turbine to the deaerator, thereby the deaerator pressure is balanced
at a lower pressure than the extraction pressure.

[0007]However, when the extraction pressure is decreased quickly
associated with a quick decay in the turbine load at the time of an
occurrence of a turbine trip, or an interruption of a load, etc, a
decompression speed of the extraction pressure exceeds that of the
deaerator pressure, and a balance between the deaerator pressure and
extraction pressure may break down. That is, the deaerator pressure may
become greater than or equal to the extraction pressure.

[0008]Also, during normal operation of the steam turbine system, when the
turbine load decays, the extraction pressure is decreased depending on
the decay rate. At this moment, the higher a decay rate of the load of
the turbine, the higher the decompression speed of the extraction
pressure.

[0009]On the other hand, regarding the deaerator having large capacity,
the more condensate stored within the deaerator, the larger a heat
capacity of the deaerator. Also, it will be difficult to decrease
deaerator temperature. As a result, it will be also difficult to decrease
the deaerator pressure.

[0010]Therefore, in the case where the capacity of the deaerator is large,
when the decay rate of the load of the steam turbine system is high and
the decompression speed of the extraction pressure is high, the
decompression speed of the extraction pressure deaerator pressure may
become lower than the decompression speed, the balance between the
deaerator pressure and extraction pressure may break down, and the
deaerator pressure may become higher than or equal to the extraction
pressure.

[0011]When the balance between the deaerator pressure and extraction
pressure breaks down and the deaerator pressure becomes higher than the
extraction pressure, a low-temperature steam flows from the deaerator to
the turbine and a water induction is generated.

[0012]Hereinafter, a flow of steam from the deaerator to the turbine is
defined as a backflow.

[0013]If the water induction is generated in the turbine, casing and rotor
of the turbine at high temperature are cooled suddenly by the
low-temperature steam, and then the casing and rotor will be deformed.
Also, a contact between a rotational body such as the rotor and a
stationary body such as the casing, or an abnormal vibration occurs, will
result in turbine damage. With those scenario, it is necessary to
suppress generation of the water induction. For this reason, it is
necessary to prevent backflow from the deaerator to the turbine.

[0014]Therefore, a check valve is conventionally provided between the
turbine and the deaerator so as to prevent the backflow from the
deaerator to the turbine.

[0015]Further, a shutdown valve device is provided so as to interrupt the
steam flow between the turbine and the deaerator.

[0016]For example, JP 11-148310 A discloses a technique for a water
induction protection device which is provided with a shutdown valve (a
shutdown valve device) to interrupt steam flow between a feedwater heater
and a turbine in a steam turbine system, and prevents water induction
occurrence when the water level of feedwater heater is increased
abnormally.

[0017]According to JP 11-148310 A, for example, if the water level of a
feedwater is increased by water leakage from a pipe inside the feedwater
heater, the shutdown valve will interrupt the steam flow between the
turbine and the feedwater heater so as to prevent water induction
occurrence.

[0018]If the technique disclosed in JP 11-148310 A is applied to the
deaerator, it is possible to prevent water induction occurrence caused by
increase in the water level within the deaerator.

[0019]By providing the check valve and shutdown valve device between the
deaerator and the turbine, it is possible to prevent water induction
occurrence caused by water level increase in the deaerator and the
backflow from the deaerator to the turbine.

SUMMARY OF THE INVENTION

[0020]However, because the check valve is instantaneously closed so as to
prevent the backflow from the deaerator to the turbine when the deaerator
pressure is greater than or equal to the extraction pressure, for
example, the check valve is instantaneously closed when the extraction
pressure decays quickly (e.g., when the turbine trip occurs). Therefore,
if the check valve is opened and closed frequently, a component such as a
valve disc may be deformed by an impact at the time of closing the check
valve, and the backflow from the deaerator to the turbine may not be
interrupted completely.

[0021]Therefore, an object of the present invention is to provide a
turbine protection device which can interrupt the backflow from the
deaerator to the turbine completely even if the check valve provided
between the deaerator and the turbine can not interrupt the steam flow
completely.

[0022]In order to achieve the above object, the present invention provides
a turbine protection device comprising: a shutdown valve device, in which
the shutdown valve device is operated so as to interrupt backflow from a
deaerator to a turbine when a deaerator pressure is greater than or equal
to the extraction pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a block diagram showing an example of a steam turbine
system;

[0024]FIG. 2 is a graph showing a status in which an extraction pressure
and a deaerator pressure are decreased;

[0025]FIG. 3 is a flowchart showing a procedure by which a control unit
controls a shutdown valve device; and

[0026]FIG. 4 is a flowchart showing a procedure by which a control unit
having an internal timer controls the shutdown valve device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027]Embodiments of the present invention will be explained in detail,
hereinafter, with reference to FIGS. 1-4.

[0028]In a steam turbine system 1 as shown in FIG. 1, the steam generated
in the boiler 13 rotates a high-pressure turbine 14, and is taken into a
reheater 13a of the boiler 13. The steam reheated by the reheater 13a
rotates a middle-pressure turbine 15 and a low-pressure turbine 16, and
is taken into a condenser 18 to be condensed into a condensate.

[0029]In addition, for example, a generator 17 is connected to the
low-pressure turbine 16 as a load.

[0030]The condensate generated by condensing the steam in the condenser 18
is pressurized by a condensate pump 19, heated by a low-pressure heater 4
(e.g., using the extraction steam from the low-pressure turbine 16), fed
to the deaerator 5, heated using the extraction steam from the
middle-pressure turbine 15 (or the low-pressure turbine 16) so as to
deaerate gases, and stored in the deaerator 5.

[0031]Then, the condensate stored in the deaerator 5 is pressurized by a
feed pump 6, heated in a high-pressure heater 7 (e.g., using the
extraction steam from the high-pressure turbine 14 or the middle-pressure
turbine 15), and taken into the boiler 13.

[0032]The high-pressure turbine 14, the middle-pressure turbine 15, and
the low-pressure turbine 16, hereinafter, are referred as turbine 2 in a
mass.

[0033]The turbine 2 is connected to the deaerator 5 via an extraction
steam inlet pipe 3 (inlet pipe), and the extraction steam from the
turbine 2 passes through the extraction steam inlet pipe 3 so as to be
taken into the deaerator 5 as the extraction steam for heating and
deaerating.

[0034]Two check valves 3a are connected to the extraction steam inlet pipe
3 in series, and a flow direction of the steam in the extraction steam
inlet pipe 3 is limited from the turbine 2 to the deaerator 5.

[0035]The extraction steam inlet pipe 3 is connected to any one or more of
the high-pressure turbine 14, the middle-pressure turbine 15, or the
low-pressure turbine 16.

[0036]Because the extraction steam from the turbine 2 is taken into the
deaerator 5 through the extraction steam inlet pipe 3, an extraction
pressure of the extraction steam from the turbine 2 (hereinafter, denoted
by "P1 ") is decreased due to a pressure loss caused by passing through
the extraction steam inlet pipe 3.

[0037]Therefore, during normal operation of the steam turbine system 1,
the deaerator pressure (hereinafter, denoted by "P2") becomes lower than
the extraction pressure P1.

[0038]Also, during normal operation of the steam turbine system 1, the
deaerator pressure P2 is balanced at a pressure which is lower than the
extraction pressure P1 so as to prevent the backflow from the deaerator 5
to the turbine 2.

[0039]Although the two check valves 3a are opened so as to allow the steam
to flow from the turbine 2 to the deaerator 5 when the deaerator pressure
P2 is less than the extraction pressure P1, the two check valves 3a are
instantaneously closed so as to interrupt the backflow from the deaerator
5 to the turbine 2 when the deaerator pressure P2 is greater than or
equal to the extraction pressure P1 when turbine trip occurs, etc.

[0040]Also, the extraction steam inlet pipe 3 is provided with a shutdown
valve device 12 between the two check valves 3a and the deaerator 5.
Shutdown valve device 12 includes a stop valve 12a to interrupt the steam
flow through the extraction steam inlet pipe 3, and a valve driving unit
12b to open and close the stop valve 12a rapidly.

[0041]The valve driving unit 12b drives the stop valve 12a so as to close
the extraction steam inlet pipe 3, to interrupt the backflow from the
deaerator 5 to the turbine 2, and to prevent occurrence of a water
induction, when water level within the deaerator 5 measured by a water
level gauge (not shown) becomes greater than a predetermined value.

[0042]Also, the steam turbine system 1 according to this embodiment
includes a turbine extraction pressure gauge 9 to measure the extraction
pressure P1 of the extraction steam from the turbine 2, deaerator
pressure gauge 10 to measure the deaerator pressure P2 of the deaerator
5, and a control unit 11 to control the shutdown valve device 12 by
sending commands to the valve driving unit 12b.

[0043]For example, the turbine extraction pressure gauge 9 is provided in
proximity to a juncture between the turbine 2 and the extraction steam
inlet pipe 3, and measures the extraction pressure P1 on condition that
the pressure loss caused by the extraction steam inlet pipe 3 does not
occur.

[0044]The control unit 11 calculates the extraction pressure P1 based on a
measured signal input from the turbine extraction pressure gauge 9, and
the deaerator pressure P2 based on a measured signal input from the
deaerator pressure gauge 10.

[0045]Also, the control unit 11 sends commands to the valve driving unit
12b to drive the stop valve 12a to close the extraction steam inlet pipe
3, when the deaerator pressure P2 becomes greater than or equal to the
extraction pressure P1. Then, the shutdown valve device 12 is closed.

[0046]Therefore, the stop valve 12a interrupts the backflow from the
deaerator 5 to the turbine 2.

[0047]After that, the deaerator pressure P2 is decreased. When the
deaerator pressure P2 becomes less than the extraction pressure P1, the
control unit 11 will send commands to the valve driving unit 12b to drive
the stop valve 12a to open the extraction steam inlet pipe 3. Then, the
shutdown valve device 12 is opened.

[0048]The extraction steam from the turbine 2 passes through the
extraction steam inlet pipe 3 so as to be taken into the deaerator 5.

[0050]As shown in FIG. 2, in condition that the deaerator pressure P2
(P2H) is lower than the extraction pressure P1 (P1H) slightly, in the
case where the steam turbine system 1 (see FIG. 1) is in normal
operation, for example, when an amount of electric-power generation
required for the generator 17 (see FIG. 1) is decreased and the load of
the turbine 2 decays, the extraction pressure P1 is decompressed to P1L
at the time t1 associated with a decay in the load.

[0051]Also, the deaerator pressure P2 is decreased to P2L at the time t2
associated with depression in the extraction pressure P1.

[0052]However, for example, in the case where the capacity of the
deaerator 5 (see FIG. 1) is large and the decay rate of the load of the
turbine 2 (see FIG. 1) is high, when the decompression speed of the
extraction pressure P1 is higher than that of the deaerator pressure P2,
for example, the extraction pressure P1 is decreased to the deaerator
pressure P2 at the time t3. After that, the deaerator pressure P2 is kept
higher than the extraction pressure P1 until the time t4 at which the
deaerator pressure P2 is decreased to P1L.

[0053]As described above, when the deaerator pressure P2 becomes greater
than or equal to the extraction pressure P1 (deaerator pressure
P2≧extraction pressure P1), two check valves 3a (see FIG. 1) are
closed so as to prevent the backflow from the deaerator 5 (see FIG. 1) to
the turbine 2 (see FIG. 1).

[0054]However, for example, in the case where the valve discs of two check
valves 3a, etc., are deformed and the steam flow through the extraction
steam inlet pipe 3 (see FIG. 1) can not be interrupted completely, the
turbine 2 may be damaged by the backflow from the deaerator 5 to the
turbine 2.

[0055]For this reason, the control unit 11 according to this embodiment
(see FIG. 1) controls the shutdown valve device 12 so that the shutdown
valve device 12 (see FIG. 1) is closed from time t5 at which a
differential pressure ΔP, which is resulted from subtracting the
extraction pressure P1 from the deaerator pressure P2 when the steam
turbine system 1 (see FIG. 1) is in normal operation, becomes greater
than or equal to the first predetermined value (ΔPf1) which is set
in advance till the time t6 at which the differential pressure ΔP
becomes less than a second predetermined value (ΔPf2) which is set
in advance.

[0056]Also, after the time t6 at which the differential pressure ΔP
becomes less than or equal to the second predetermined value ΔPf2,
the control unit 11 controls the shutdown valve device 12 to be closed.

[0057]When the differential pressure ΔP becomes greater than or
equal to the first predetermined value ΔPf1 which is resulted from
subtracting the extraction pressure P1 from the deaerator pressure P2,
the control unit 11 will send commands to the valve driving unit 12b (see
FIG. 1) so that the stop valve 12a (see FIG. 1) closes the extraction
steam inlet pipe 3 so as to close the shutdown valve device 12 (see FIG.
1).

[0058]And, when the differential pressure ΔP becomes less than or
equal to the second predetermined value ΔPf2, the control unit 11
will send commands to the valve driving unit 12b so that the stop valve
12a opens the extraction steam inlet pipe 3 so as to open the shutdown
valve device 12.

[0059]In this way, the control unit 11 controls the shutdown valve device
12 by sending commands based on the differential pressure ΔP
between the deaerator pressure P2 and the extraction pressure P1.

[0060]For example, considering measurement errors of the turbine
extraction pressure gauge 9 and deaerator pressure gauge 10, and changes
(microseisms) in the deaerator pressure P2 and extraction pressure P1,
etc., the first predetermined value ΔPf1 and second predetermined
value ΔPf2 are set to values as small as possible. The first
predetermined value ΔPf1 may differ from or may be the same as the
second predetermined value ΔPf2.

[0061]Also, the first predetermined value ΔPf1 and second
predetermined value ΔPf2 may be "0".

[0062]In the case where the first predetermined value ΔPf1 is "0",
the control unit 11 closes the shutdown valve device 12 (see FIG. 1) when
the deaerator pressure P2 becomes greater than or equal to the extraction
pressure P1. In the case where the second predetermined value ΔPf2
is "0", the control unit 11 opens the shutdown valve device 12 (see FIG.
1) when the extraction pressure P1 becomes greater than or equal to the
deaerator pressure P2.

[0063]In addition, the first predetermined value ΔPf1 and second
predetermined value ΔPf2 are set as differential pressures resulted
from subtracting the extraction pressure P1 from the deaerator pressure
P2. Therefore, in the case the extraction pressure P1 is higher than the
deaerator pressure P2, the first predetermined value ΔPf1 and
second predetermined value ΔPf2 become negative values.

[0064]With reference to FIG. 3, a procedure by which the control unit 11
controls the shutdown valve device 12 will be explained (see FIGS. 1 and
2).

[0065]For example, this procedure is incorporated in a program which the
control unit 11 runs as a subroutine, and may be run by the control unit
11 at intervals of 100 ms, etc.

[0066]When the procedure to control the shutdown valve device 12 starts,
the control unit 11 calculates the extraction pressure P1 (step S1), and
further calculates the deaerator pressure P2 (step S2).

[0067]As described above, the control unit 11 can calculate the extraction
pressure P1 based on the measured signal input from the turbine
extraction pressure gauge 9, and can calculate the deaerator pressure P2
based on the measured signal input from the deaerator pressure gauge 10.

[0068]In this way, the control unit 11 calculates the extraction pressure
P1 and deaerator pressure P2 at every time the procedure to control the
shutdown valve device 12 is executed. Therefore, the control unit 11
monitors the extraction pressure P1 and deaerator pressure P2 at all
times.

[0070]Also, when the calculated differential pressure ΔP is greater
than or equal to the first predetermined value ΔPf1 (step
S4→Yes), if the shutdown valve device 12 is opened (step
S5→Yes), the control unit 11 will send commands to the valve
driving unit 12b to drive the stop valve 12a to close the shutdown valve
device 12 (step S6), and the procedure to control the shutdown valve
device 12 is completed (RETURN). If the shutdown valve device 12 is not
opened (step S5→No), i.e., if the shutdown valve device 12 is
closed, the procedure to control the shutdown valve device 12 is
completed (RETURN).

[0071]On the other hand, when the calculated differential pressure
ΔP is less than the first predetermined value ΔPf1 (step S4
→No), if the differential pressure ΔP is greater than the
second predetermined value ΔPf2 (step S7→No), the control
unit 11 completes the procedure to control the shutdown valve device 12
(RETURN).

[0072]Also, when the differential pressure ΔP is less than or equal
to the second predetermined value ΔPf2 (step S7→Yes), and if
the shutdown valve device 12 is closed (step S8→Yes), the control
unit 11 will send commands to the valve driving unit 12b to drive the
stop valve 12a to open the shutdown valve device 12 (step S9), and
completes the procedure to control the shutdown valve device 12 (RETURN).
If the shutdown valve device 12 is not closed (step S8→No), i.e.,
if the shutdown valve device 12 is open, the procedure to control the
shutdown valve device 12 is completed (RETURN).

[0073]The method by which the control unit 11 judges whether the shutdown
valve device 12 is opened or closed is not limited.

[0074]For example, the control unit 11 may includes a flag OP to indicate
whether the shutdown valve device 12 is opened or closed, and the control
unit 11 sets the flag OP to "0" in step S6 when the shutdown valve device
12 is closed and sets the flag OP to "1" in step S9 when the shutdown
valve device 12 is opened.

[0075]The control unit 11 judges that the shutdown valve device 12 is
opened if the flag OP is "1", and judges that the shutdown valve device
12 is closed if the flag OP is "0".

[0076]Also, the shutdown valve device 12 may be provided with a sensor
(not shown) to detect whether the stop valve 12a closes or opens the
extraction steam inlet pipe 3. For example, if the sensor (not shown)
sends a detection signal to indicate whether the stop valve 12a closes or
opens the extraction steam inlet pipe 3 to the control unit 11, the
control unit 11 can detect whether the stop valve 12a closes or opens the
extraction steam inlet pipe 3 based on the detection signal from the
sensor (not shown). Also, the control unit 11 can judge whether the
shutdown valve device 12 is opened or closed.

Modified Example

[0077]As described above, the control unit 11 of the steam turbine system
1 according to this embodiment shown in FIG. 1 monitors the extraction
pressure P1 and deaerator pressure P2 at all times, closes the shutdown
valve device 12 when the differential pressure ΔP resulted from
subtracting the extraction pressure P1 from the deaerator pressure P2
becomes greater than or equal to the first predetermined value
ΔPf1, and opens the shutdown valve device 12 when the differential
pressure ΔP becomes less than or equal to the second predetermined
value ΔPf2.

[0079]Therefore, the extraction pressure P1 and deaerator pressure P2
calculated by the control unit 11 can also slightly change, and further
the differential pressure ΔP resulted from subtracting the
extraction pressure P1 from the deaerator pressure P2 can also slightly
change.

[0080]If the differential pressure ΔP changes across the first
predetermined value ΔPf1 and second predetermined value ΔPf2,
the control unit 11 will send commands to the valve driving unit 12b to
close the shutdown valve device 12 at every time the differential
pressure ΔP becomes greater than or equal to the first
predetermined value ΔPf1, and will send commands to the valve
driving unit 12b to open the shutdown valve device 12 at every time the
differential pressure ΔP becomes less than or equal to the second
predetermined value ΔPf2. Therefore, the control unit 11 frequently
sends commands to the valve driving unit 12b to control the shutdown
valve device 12, and the shutdown valve device 12 is opened and closed
frequently. As a result, there arises a problem that the stop valve 12a
and the shutdown valve device 12 are degraded.

[0081]For this reason, in a modified example of the present invention, for
example, the control unit 11 may be provided with an internal timer, and
may close the shutdown valve device 12 when a condition that the
differential pressure ΔP resulted from subtracting the extraction
pressure P1 from the deaerator pressure P2 is greater than or equal to
the first predetermined value ΔPf1 continues for a predetermined
time period.

[0082]Likewise, when a condition that the differential pressure ΔP
resulted from subtracting the extraction pressure P1 from the deaerator
pressure P2 is less than or equal to the second predetermined value
ΔPf2 continues for a predetermined time period, the control unit 11
may open the shutdown valve device 12.

[0083]With reference to FIG. 4, a procedure by which the control unit 11
having the internal timer controls the shutdown valve device 12 (see
FIGS. 1 and 2).

[0084]Like the procedure shown in FIG. 3, this procedure is incorporated
in a program which the control unit 11 runs as a subroutine, and may be
run by the control unit 11 at intervals of 100 ms, etc.

[0085]In addition, the same reference numbers are used to denote the same
steps as those in FIG. 3, and their repeated explanations will be
omitted.

[0087]Also, when the calculated differential pressure ΔP is greater
than or equal to the first predetermined value ΔPf1 (step
S4→Yes), the control unit 11 stops measuring opening valve waiting
time (step S10), and if the shutdown valve device 12 is opened (step
S5→Yes), the control unit 11 judges whether a closing valve
waiting time is being measured or not (step S11).

[0088]The opening valve waiting time means waiting time during the
differential pressure ΔP resulted from subtracting the extraction
pressure P1 from the deaerator pressure P2 becomes less than or equal to
the second predetermined value ΔPf2 and the control unit 11 opens
the shutdown valve device 12.

[0089]Also, the closing valve waiting time means waiting time during the
differential pressure ΔP resulted from subtracting the extraction
pressure P1 from the deaerator pressure P2 becomes greater than or equal
to the first predetermined value ΔPf1 and the control unit 11
closes the shutdown valve device 12.

[0090]Also, if the closing valve waiting time is not being measured (step
S11→No), the control unit 11 starts measuring the closing valve
waiting time by the internal timer (step S12), and the procedure to
control the shutdown valve device 12 is completed (RETURN).

[0091]Also, if the closing valve waiting time is being measured (step
S11→Yes), in the case where a predetermined time Tm1 (a first
predetermined time) has elapsed since measuring the closing valve waiting
time started (step S13→Yes), the control unit 11 closes the
shutdown valve device 12 (step S6) and completes the procedure to control
the shutdown valve device 12 (RETURN), and in the case where the
predetermined time Tm1 has not elapsed (step S13→No), the control
unit 11 completes the procedure to control the shutdown valve device 12
(RETURN) without closing the shutdown valve device 12.

[0092]Returning to step S5, if the shutdown valve device 12 is not opened
(step S5 →No), i.e., if the shutdown valve device 12 is closed,
the control unit 11 completes the procedure to control the shutdown valve
device 12 (RETURN).

[0093]In step S13, for example, the predetermined time Tm1 to determine
whether the shutdown valve device 12 should be closed or not may be
determined as a time during which the control unit 11 can close the
shutdown valve device 12 with the proper timing based on an experiment,
etc.

[0094]Returning to step S4, when the calculated differential pressure
ΔP is less than the first predetermined value ΔPf1 (step
S4→No), the control unit 11 compares the differential pressure
ΔP and the second predetermined value ΔPf2 (step S7). Also,
when the differential pressure ΔP is greater than the second
predetermined value ΔPf2 (step S7→No), the control unit 11
completes the procedure to control the shutdown valve device 12 (RETURN).

[0095]Also, when the differential pressure ΔP is less than or equal
to the second predetermined value ΔPf2 (step S7→Yes), the
control unit 11 stops the measuring the closing valve waiting time (step
S14). If the shutdown valve device 12 is closed (step S8→Yes), the
control unit 11 judges whether the opening valve waiting time is being
measured or not (step S15).

[0096]In addition, when the shutdown valve device 12 is not closed (step
S8→No), i.e., when the shutdown valve device 12 is opened, the
control unit 11 completes the procedure to control the shutdown valve
device 12 (RETURN).

[0097]Also, if the opening valve waiting time is not being measured (step
S15→No), the control unit 11 starts measuring the opening valve
waiting time by the internal timer (step S16), and completes the
procedure to control the shutdown valve device 12 (RETURN). Also, if the
opening valve waiting time is being measured (step S15→Yes), in
the case where the predetermined time Tm2 (a second predetermined time)
has elapsed since measuring the opening valve waiting time started (step
S17→Yes), the control unit 11 closes the shutdown valve device 12
(step S9) and completes the procedure to control the shutdown valve
device 12 (RETURN), and in the case where the predetermined time Tm2 has
not elapsed (step S17→No), the control unit 11 completes the
procedure to control the shutdown valve device 12 (RETURN) without
opening the shutdown valve device 12.

[0098]In step S17, for example, the predetermined time Tm2 to determine
whether the shutdown valve device 12 should be opened or not may be
determined as a time during which the control unit 11 can open the
shutdown valve device 12 with the proper timing based on an experiment,
etc., and may be the same as or differ from the predetermined time Tm1 in
step S13.

[0099]As shown in FIG. 4, in the modified example, when the differential
pressure ΔP resulted from subtracting the extraction pressure P1
from the deaerator pressure P2 is greater than or equal to the first
predetermined value ΔPf1, the control unit 11 (see FIG. 1) starts
measuring the closing valve waiting time by the internal timer (step
S12), and when the predetermined time Tm1 has elapsed on condition that
the differential pressure ΔP is greater than or equal to the first
predetermined value ΔPf1, the control unit 11 closes the shutdown
valve device 12 (see FIG. 1)(step S13). In this way, after the
differential pressure ΔP resulted from subtracting the extraction
pressure P1 from the deaerator pressure P2 becomes greater than or equal
to the first predetermined value ΔPf1, and when the predetermined
time Tm1 (the first predetermined time) has elapsed on condition that the
differential pressure ΔP is greater than or equal to the first
predetermined value ΔPf1, the control unit 11 closes the shutdown
valve device 12.

[0100]Also, when the differential pressure ΔP resulted from
subtracting the extraction pressure P1 from the deaerator pressure P2 is
less than or equal to the second predetermined value ΔPf2, the
control unit 11 (see FIG. 1) starts measuring the opening valve waiting
time by the internal timer (step S16), and when the predetermined time
Tm2 has elapsed on condition that the differential pressure ΔP is
less than or equal to the second predetermined value ΔPf2, the
control unit 11 opens the shutdown valve device 12 (see FIG. 1)(step
S17). In this way, after the differential pressure ΔP resulted from
subtracting the extraction pressure P1 from the deaerator pressure P2
becomes less than or equal to the second predetermined value ΔPf2,
and when the predetermined time Tm2 (the second predetermined time) has
elapsed on condition that the differential pressure ΔP is less than
or equal to the second predetermined value ΔPf2, the control unit
11 will close the shutdown valve device 12.

[0101]Also, associated with changes in measured values of the turbine
extraction pressure gauge 9 and deaerator pressure gauge 10, in the case
where the differential pressure ΔP calculated by the control unit
11 changes across the first predetermined value ΔPf1 at intervals
shorter than the predetermined time Tm1, even if the differential
pressure ΔP is greater than or equal to the first predetermined
value ΔPf1, the control unit 11 does not close the shutdown valve
device 12.

[0102]Likewise, even if differential pressure ΔP is less than or
equal to the second predetermined value ΔPf2, the control unit 11
does not open the shutdown valve device 12, in the case where the
differential pressure ΔP calculated by the control unit 11 changes
across the second predetermined value ΔPf2 at intervals shorter
than the predetermined time Tm2.

[0103]Therefore, the shutdown valve device 12 is prevented from being
operated frequently to suppress the problem that the shutdown valve
device 12 is degraded.

[0104]As described above, in the turbine protection device 20 of the steam
turbine system 1 according to this embodiment shown in FIG. 1, the
control unit 11 monitors the extraction pressure P1 and deaerator
pressure P2 at all times. When the differential pressure ΔP
resulted from subtracting the extraction pressure P1 from the deaerator
pressure P2 is greater than or equal to the first predetermined value
ΔPf1, the control unit 11 closes the shutdown valve device 12 to
interrupt the backflow from the deaerator 5 to the turbine 2 by the stop
valve 12a.

[0105]When the deaerator pressure P2 becomes greater than or equal to the
extraction pressure P1, two check valves 3a are closed so as to interrupt
the backflow from the deaerator 5 to the turbine 2.

[0106]However, if the valve disc of two check valves 3a, etc. are deformed
and these two check valves 3a can not interrupt the steam flow through
the extraction steam inlet pipe 3 completely, the turbine 2 may be
damaged by the backflow from the deaerator 5 to the turbine 2.

[0107]Even if two check valves 3a can not interrupt the steam flow through
the extraction steam inlet pipe 3 completely, the steam turbine system 1
according to this embodiment can interrupt the steam flow through the
extraction steam inlet pipe 3 by the stop valve 12a of the shutdown valve
device 12, and can interrupt the backflow from the deaerator 5 to the
turbine 2 effectively.

[0108]Also, after the differential pressure ΔP resulted from
subtracting the extraction pressure P1 from the deaerator pressure P2
becomes greater than or equal to the first predetermined value
ΔPf1, and when the predetermined time Tm1 has elapsed, the control
unit 11 closes the shutdown valve device 12. After the differential
pressure ΔP becomes less than or equal to the second predetermined
value ΔPf2, when the predetermined time Tm2 has elapsed, the
control unit 11 opens the shutdown valve device 12.

[0109]In this way, the shutdown valve device 12 is prevented from being
operated frequently to suppress the problem that the shutdown valve
device 12 is degraded.

[0110]In addition, even if the deaerator pressure P2 becomes greater than
or equal to the extraction pressure P1 associated with a quick decay in a
load of the steam turbine system 1, the control unit 11 can close the
shutdown valve device 12, not only at the time of normal operation of the
steam turbine system 1 but also at the time of an occurrence of a turbine
trip, or an interruption of a load, etc,. Therefore, even if two check
valves 3a can not interrupt the steam flow through the extraction steam
inlet pipe 3 completely, the backflow from the deaerator 5 to the turbine
2 can be interrupted completely, and the turbine 2 can be prevented from
being damaged.

[0111]Although the turbine protection device 20 is provided between the
deaerator 5 and the turbine 2 in this embodiment as shown in FIG. 1, for
example, the turbine protection device 20 according to this embodiment
may be provided also between the feedwater heater (not shown) and the
turbine 2.

[0112]In this case, even if the pressure within the feedwater heater
becomes higher than the extraction pressure P1, the backflow from the
feedwater heater to the turbine 2 can be interrupted by the stop valve
12a, and the turbine 2 can be prevented from being damaged.